Method for manufacturing a corrosion sensor

ABSTRACT

A method for manufacturing a corrosion sensor includes spraying a non-conductive material on a substrate and spraying a conductive material at discrete locations on the substrate or on the non-conductive material. The method further includes spraying the non-conductive material around the discrete locations of the conductive material.

FIELD OF THE INVENTION

The present invention generally involves a method for manufacturing acorrosion sensor.

BACKGROUND OF THE INVENTION

Machinery and equipment operated in harsh environments are often subjectto accelerated corrosion rates which, if not monitored or controlled,can result in premature aging and eventually failure of the machineryand equipment. For example, in a gas turbine, high temperaturecombustion gases flow along a hot gas path through a turbine to producework. The combustion gases may include sufficient quantities of oxygento produce general corrosion on the metal surfaces along the hot gaspath. The general corrosion is characterized by an oxidation-reductionreaction in which the metal surfaces are oxidized, producing an anode atthe oxidation site and a cathode at the reduction site.

Sensors may be installed on the metal surfaces to monitor the presenceand/or rate of any general corrosion. For example, as shown in FIG. 1, aconventional corrosion sensor 10 installed on a metal surface 12 maycomprise alternating layers of electrodes 14 separated by dielectricmaterial 16. The electrodes 14 may have an oxidation potentialcomparable to that of the metal surfaces 12 so that the generalcorrosion rate on the metal surfaces 12 may be approximated by thegeneral corrosion rate on the electrodes 14. The general corrosion rateoccurring on the metal surfaces 12 may thus be determined using a sensor18 to measure the electrical potential or current flow across theelectrodes 14.

The bond or interface between the electrodes 14 and the dielectricmaterial 16 in the conventional corrosion sensor 10 may degrade overtime, creating small gaps 19 or other low flow regions between theelectrodes 14 and dielectric material 16, as shown in FIG. 1. These gaps19 or low flow regions result in a local area conducive to crevicecorrosion. Crevice corrosion between the electrodes 14 and dielectricmaterial 16 exposes a larger surface area of the electrodes 14 to thehot gas path, increasing the electrical potential or current flow acrossthe electrodes 14 for the same general corrosion rate. As a result,crevice corrosion changes the calibration and/or accuracy of theconventional corrosion sensors 10 over time. Therefore, a corrosionsensor and method for manufacturing a corrosion sensor resistive tocrevice corrosion would be useful.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention are set forth below in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

One embodiment of the present invention is a method for manufacturing acorrosion sensor. The method includes spraying a non-conductive materialon a substrate and spraying a conductive material at discrete locationson the substrate or on the non-conductive material. The method furtherincludes spraying the non-conductive material around the discretelocations of the conductive material.

Another embodiment of the present invention is a method formanufacturing a corrosion sensor that includes spraying a non-conductivematerial on a substrate and spraying a conductive material at discretelocations on the substrate or on the non-conductive material. The methodfurther includes determining the thickness of the conductive material atdiscreet locations and spraying the non-conductive material around thediscrete locations of the conductive material.

Those of ordinary skill in the art will better appreciate the featuresand aspects of such embodiments, and others, upon review of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is a simplified side cross-section view of a conventionalcorrosion sensor;

FIG. 2 is a simplified side cross-section view of a corrosion sensoraccording to one embodiment of the present invention;

FIG. 3 is a top plan view of the corrosion sensor shown in FIG. 2;

FIG. 4 is a simplified side cross-section view of a direct writedeposition system for manufacturing a corrosion sensor according to oneembodiment of the present invention;

FIG. 5 is a flow diagram of a method for manufacturing corrosion sensorsaccording to one embodiment of the present invention;

FIG. 6 is a flow diagram of a method for manufacturing a corrosionsensor according to a second embodiment of the present invention; and

FIG. 7 is a flow diagram of a method for manufacturing a corrosionsensor according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention.

Each example is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that modifications and variations can be made in thepresent invention without departing from the scope or spirit thereof.For instance, features illustrated or described as part of oneembodiment may be used on another embodiment to yield a still furtherembodiment. Thus, it is intended that the present invention covers suchmodifications and variations as come within the scope of the appendedclaims and their equivalents.

Embodiments of the present invention provide a corrosion sensor andmethods for manufacturing the corrosion sensor that is believed to bemore sensitive to detecting and measuring general corrosion and/or moreresistant to crevice corrosion known to degrade the sensitivity andaccuracy of conventional corrosion sensors. The various embodimentsgenerally benefit from direct write deposition techniques that allow forthe repeatable and reliable production of smaller electrodes that arespaced closer together. In addition, the direct write depositiontechniques employed by embodiments of the present invention produce agenerally seamless interface or joint between the conducting portionsand non-conducting portions of the corrosion sensor to reduce and/orprevent crevice corrosion from degrading the corrosion sensor over time.

FIG. 2 provides a simplified side cross-section view of a corrosionsensor 20 according to one embodiment of the present invention, and FIG.3 provides a simplified top plan view of the corrosion sensor 20 shownin FIG. 2. The corrosion sensor 20 is designed to be installed in or ona metallic substrate 22 to monitor and/or measure the presence or rateof general corrosion occurring on the metallic substrate 22. Duringoperations, the corrosion sensor 20 experiences general corrosion atapproximately the same rate as the metallic substrate 22, and thecurrent flow and/or electrical potential produced by the corrosionsensor 20 may be measured to determine the general corrosion rate of themetallic substrate 22.

As shown, a particular embodiment of the corrosion sensor 20 may includea plurality of conductive portions 24, at least one non-conductiveportion 26, and a seamless joint 28 between the conductive andnon-conductive portions 24, 26. The conductive portions 24 may compriseplatinum, palladium, gold, silver, copper, combinations or blendsthereof, or other highly conductive materials known in the art. Inaddition, the conductive portions 24 may be doped with additionalmaterials so that the conductive portions 24 have an oxidation potentialcomparable to the metallic substrate 22. Although depicted ascylindrical in shape, the conductive portions 24 may take any geometricshape. The at least one non-conductive portion 26 may surround andelectrically insulate the conductive portions 24 and may comprise anynon-conductive material suitable for the temperatures and pressuresanticipated for the metallic substrate 22. For example, thenon-conductive portion(s) 26 may comprise dielectric material, ceramics,or other suitable non-conductive materials known in the art. Themanufacturing methods disclosed herein generally allow fabrication ofsmaller and more closely spaced conductive portions 24 than inconventional corrosion sensors. For example, the conductive portions 24manufactured according to various embodiments of the present inventionmay have a dimension exposed to general corrosion of less thanapproximately 500 microns, and in some embodiments as small asapproximately 5 microns. Alternately, or in addition, the spacingbetween adjacent conductive portions 24 may result in the non-conductiveportion 26 between adjacent conductive portions 24 having a dimensionless than approximately 500 microns, and in some embodiments as small asapproximately 5 microns.

The seamless joint 28 or connection between the conductive andnon-conductive portions 24, 26 reduces and/or prevents crevice corrosionfrom occurring between the conductive and non-conductive portions 24,26. The seamless joint 28 may comprise, for example, a metallurgicalbond such as a brazed joint between the conductive and non-conductiveportions 24, 26.

The corrosion sensor 20 may be attached directly to the metallicsubstrate 22, for example, by an adhesive material. Alternatively, asshown in FIG. 2, an optional bond coat layer 30 may be included betweenthe corrosion sensor 20 and the metallic substrate 22 to minimize anychemical or electrical interaction between the corrosion sensor 20 andthe metallic substrate 22 and/or to provide improved adhesion betweenthe corrosion sensor 20 and the metallic substrate 22. The optional bondcoat layer 30 may comprise, for example, alumina, a thermal barriercoating, or another layer to enhance the adherence between the corrosionsensor 20 and the metallic substrate 22. As shown in FIGS. 2 and 3,electrodes 32 may connect each conductive portion 24 to an electricalsensor 34. The electrodes 32 may comprise a conductive wire, perhapsformed from the same conductive material and in the same manner as theconductive portions 24, and may be embedded in the corrosion sensor 20for conducting current flow between the conductive portions 24 and theelectrical sensor 34. The electrical sensor 34 may comprise a voltmeter,an ammeter, or another suitable sensor for measuring the electricalpotential and/or current flow between the conductive portions 24. Inthis manner, the voltage or current flow between the conductive portions24 may be used to determine the general corrosion rate of the substratematerial 22.

The corrosion sensor 20 described and illustrated in FIGS. 2 and 3 maybe manufactured using one of several direct write deposition techniques.As used herein, “direct write deposition techniques” include dip pennanolithography, micropen writing, laser particle guidance or laser jetprinting, plasma spraying, laser assisted chemical vapor deposition, inkjet printing, and transfer printing, any of which may be adapted tomanufacture corrosion sensors 20 within the scope of the presentinvention. For example, FIG. 4 shows a direct write deposition system 40for manufacturing corrosion sensors 20 according to various embodimentsof the present invention. As shown, the system 40 may include aplurality of nozzles 42 directed at a work piece 44, with relativemotion between the nozzles 42 and the work piece 44. For example, thenozzles 42 may be attached to one or more arms 46 or assembliesconfigured to move each nozzle 42 with respect to the stationary workpiece 44. Alternatively, or in addition, the work piece 44 may belocated on a conveyor 48 or other surface configured to move the workpiece 44 with respect to the nozzles 42.

Each nozzle 42 may be connected to a separate supply of materialdedicated to that particular nozzle 42. Alternately, multiple suppliesof materials may be multiplexed through a single nozzle 42. Each supplyof material may include a pump, a container 50, a mixer, and otherassociated equipment for supplying the material to be deposited onto thework piece 44. The material to be deposited may comprise fine powdersranging in size on the order of 10 nanometers to several hundredmicrons. The fine powders may be suspended in a solvent, such as alcoholor water, that may further include fillers or binders such as starch,cellulose, surfactants, and other additives to adjust the rheologicalproperties of the material. The nozzle diameter and rheology of thesupplied material generally determine the minimum and maximum dimensionsof the deposited material. For example, nozzles 42 having a diameter of25-600 microns may readily produce deposits in dimensions ranging fromapproximately 1-600 microns in width and 1-10 microns in thickness perpass, with the number of passes dependent on the desired thickness ofthe deposited material.

As shown in FIG. 4, for example, the system 40 may include separatenozzles 42 dedicated for depositing non-conductive material 52,conductive material 54, and brazing material 56 onto the work piece 44.As the nozzles 42 move with respect to the work piece 44, a controller(not shown) may execute a CAD/CAM or similar program to actuate eachnozzle 42 as desired to deposit the specific material onto discretelocations on the work piece 44. For example, the controller may actuatethe nozzles 42 to sequentially deposit the non-conductive material 52,conductive material 54, and brazing material 56 onto the bond coat 30during multiple passes to form the corrosion sensor 20 as shown in FIG.4. The resulting deposition layers may be cured between successivepasses of the nozzles 42 or when the desired thicknesses are achievedusing conventional curing devices, such as, for example, ovens, lamps,and other heat sources. Alternately, as shown in FIG. 4, a source 58 maybe integrated with the system 40 to cure the resulting deposition layerand/or braze the conductive and non-conductive portions 24, 26 using,for example, ultraviolet, ultrasonic, thermal, or other forms of heat.

Multiple variations of the exemplary direct write system 40 shown inFIG. 4 may be used to manufacture corrosion sensors 20 within the scopeof the present invention. For example, the system 40 may include onenozzle supplied with the non-conductive filler material 52 to beinfiltrated, a second nozzle supplied with the conductive material 54 orslurry, and a third nozzle supplied with the brazing material 56 orslurry. The first nozzle may thus deposit a uniform base coat of thefiller material 52 onto the bond coat 30, if present, or metallicsubstrate 22 during an initial pass or series of passes. The secondnozzle may then deposit the conductive material 54 at discrete locationsto mix with the filler material 52 in the base coat, and the thirdnozzle may deposit the brazing material 56 around each discrete locationof the conductive material 54. Sintering or other curing may then beperformed to the resulting deposition layers to produce any of thecorrosion sensors 20 illustrated in FIGS. 2-4.

Method 1: FIG. 5 provides a flow diagram of a first method formanufacturing corrosion sensors 20, for example using the system 40described and shown in FIG. 4. At block 60, a thin layer ofnon-conductive or filler material 52 may be deposited, sprayed, printed,or otherwise applied to the substrate, such as, for example the bondcoat 30 or directly to the metallic substrate 22 being monitored forcorrosion. At block 62, during the same or subsequent passes, a thinlayer of conductive or binder material 54 may similarly be deposited,sprayed, printed, or otherwise applied at specific or discretelocations, and at block 64, a brazing material 56 may be deposited,sprayed, printed, or otherwise applied around each discrete location ofthe conductive or binder material 54.

One of ordinary skill in the art will readily appreciate that one ormore of the filler material 52, binder material 54, and/or brazingmaterial 56 may be applied as a dry nano-powder, a liquid, or a slurryof fine powders suspended in a solvent, such as alcohol or water, thatmay further include fillers or binders such as starch, cellulose,surfactants, and other additives to adjust the rheological properties ofthe material. In addition, the non-conductive or filler material 52, theconductive or binder material 54, and/or the brazing material 56 may beselected or doped to have similar melting points to one another. In thismanner, the nozzles 42 may deposit, spray, print, or otherwise apply theconductive or binder material 54 to produce conductive portions 24having a dimension of less than approximately 500 microns, and in someembodiments as small as approximately 5 microns. In addition, thespacing between adjacent conductive portions 24 may result in thenon-conductive portion 26 between adjacent conductive portions 24 havinga dimension less than approximately 500 microns, and in some embodimentsas small as approximately 5 microns.

At block 66, the source 58 may be energized to cure the previouslyapplied filler material 52, binder material 54, and/or brazing material56, for example such as by using ultraviolet, ultrasonic, thermal, orother forms of heat appropriate for the particular filler, binder, andbrazing materials 52, 54, 56 being used. Curing of the non-conductive orfiller material 52 produces the non-conductive portions 26. Curing ofthe conductive or binder material 54 mixed with the filler material 52produces the conductive portions 24 and/or electrodes 32. Curing of thebrazing material 56 around each discrete location of the conductive orbinder material 54 produces the seamless joint or metallurgical bond 28between the conductive and non-conductive portions 24, 26.

At block 68, the thickness of the various layers are checked, and one ormore of blocks 60, 62, 64 and/or 66 may be repeated, as desired, toincrease the thickness of the conductive portions 24, non-conductiveportions 26, and/or seamless joint 28 on the corrosion sensor 20. Oncethe desired thickness of each layer is achieved, the process continuesto block 70 where electrodes 32, if not previously formed in concertwith the conductive portions 24, may be connected to each discretelocation of the conductive material 24. If desired, the electrodes 32may be pretreated or conditioned to create an adherent oxide layerresistant to crevice corrosion on the surface of the electrodes, asrepresented by block 72. The pretreatment or conditioning of theelectrodes 32 may take place after each layer is applied to thesubstrate. Alternately, the pretreatment or conditioning of theelectrodes 32 may take place as a final finishing process. At block 74,the electrodes 32 may be connected to the electrical sensor 34 so thatthe electrical sensor 34 is connected to each discrete location of theconductive material 24.

Method 2: FIG. 6 provides a flow diagram of a method for manufacturingcorrosion sensors 20 according to a second embodiment of the presentinvention. At block 80, a first layer of non-conductive material 26 maybe deposited, sprayed, printed, or otherwise applied to the substrate.The substrate may comprise, for example, the bond coat 30 or themetallic substrate 22 being monitored for corrosion and may alreadyinclude electrodes 32 pre-positioned at desired locations to connect tothe subsequently applied conductive portions 24. At block 82, theconductive portions 24 may be written onto the non-conductive material26 in particular locations in a manner similar to writing with an inkpen. For example, a metal in solution, such as a molten metal or a metalpowder in a liquid solution, may be written onto the non-conductivematerial 26 to form the desired patterns of the conductive portions 24.As previously described, the specific locations of the conductiveportions 24 may result in a dimension of less than approximately 500microns, and in some embodiments as small as approximately 5 microns. Inaddition, the spacing between adjacent conductive portions 24 may resultin the non-conductive portion 26 between adjacent conductive portions 24having a dimension less than approximately 500 microns, and in someembodiments as small as approximately 5 microns.

At block 84, the resulting conductive and non-conductive portions 24, 26may be cured, for example using ultraviolet, ultrasonic, thermal, orother forms of heat appropriate for the particular materials being used.At block 86, the thickness of the various layers is checked. If desired,the writing (block 82) and/or curing (block 84) process may be repeatedwith additional layers of the metal repeatedly written onto thepreviously cured conductive portions 24 to build up the conductiveportions 24 at specific locations to be thicker than the underlyingelectrodes 32 being used.

When the desired thickness of the conductive portions 24 is achieved,the process continues to block 88 where a second or final layer of thenon-conductive material 26 may be applied over the entire surface,covering both the conductive and non-conductive portions 24, 26. A finalcuring step may be repeated, if desired. At block 90, a portion of thesecond or final layer of the non-conductive material 26 may be lightlymachined to expose the surface of the conductive portions 24 withoutexposing the underlying electrodes 32. At block 92, the electricalsensor 34 may be connected to each of the conductive portions 24 and/orelectrodes 32 to produce the corrosion sensor 20 with the seamless joint28 between the conductive and non-conductive portions 24, 26.

Method 3: FIG. 7 provides a flow diagram of a method for manufacturingcorrosion sensors 20 according to a third embodiment of the presentinvention. In this particular method, the corrosion sensors 20 may beformed using thermal spray or cold spray techniques, such as, forexample, high velocity oxy-fuel, thermal spray, or cold spraytechniques. Specifically, at block 100, the non-conductive material 26may be sprayed onto the substrate using a thermal spray or cold spraytechnique known in the art. The substrate may again comprise, forexample, the bond coat 30 or the metallic substrate 22 being monitoredfor corrosion and may already include electrodes 32 at desired locationsto connect to the subsequently applied conductive portions 24. At block102, the conductive portions 24 may be sprayed onto the substrate and/ornon-conductive material 26 in particular locations to achieve thedesired pattern or spacing of conductive and non-conductive portions 24,26 across the substrate, as previously described with respect to Methods1 and 2. Specifically, the specific locations of the conductive portions24 may result in a dimension of less than approximately 500 microns, andin some embodiments as small as approximately 5 microns. In addition,the spacing between adjacent conductive portions 24 may result in thenon-conductive portion 26 between adjacent conductive portions 24 havinga dimension less than approximately 500 microns, and in some embodimentsas small as approximately 5 microns. At block 104, the non-conductivematerial 26 may be sprayed around the previously applied conductiveportions 24 to fill the space between the conductive portions 24 anddiffuse with the conductive portions 24 to form the seamless bond 28between the conductive and non-conductive portions 24, 26.

At block 106, the thickness of the sensor 20, particularly the thicknessof the conductive material 24 at discrete locations, is checked. Ifdesired, the process of spraying conductive portions 24 at discretelocations (block 102) and non-conductive portions 26 around theconductive portions 24 (block 104) may be repeated as necessary toachieve a desired thickness of the conductive and non-conductiveportions 24, 26. When the desired thickness of the conductive andnon-conductive portions 24, 26 is achieved, the process continues toblock 108 where the electrical sensor 34 may be connected to each of theconductive portions 24 or electrodes 32 to produce the corrosion sensor20 with the seamless bond 28 between the conductive and non-conductiveportions 24, 26.

It is believed that one or more of the previously described direct writedeposition techniques will allow the manufacture of corrosion sensors 20within the scope of the present invention with one or more benefits overthe existing technology. For example, the techniques described hereinwill allow for the repeatable, cost-effective production of corrosionsensors 20 having smaller conductive portions 24 capable of detectingand/or measuring smaller amounts of aqueous or molten salt corrosion.The smaller sized corrosion sensors 20 will also be suitable for smallerenvironments that were previously too small to accommodate a corrosionsensor. In addition, the seamless metallurgical joint 28 between theconductive and non-conductive portions 24, 26 reduces the occurrence ofcrevice corrosion to enhance the accuracy and reliability of thecorrosion sensors 20 over time.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other and examples areintended to be within the scope of the claims if they include structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal languages of the claims.

What is claimed is:
 1. A method for manufacturing a corrosion sensorcomprising: a. spraying a non-conductive material on a bond coat that isapplied to a metallic substrate; b. spraying a conductive material atdiscrete locations on the bond coat or on the non-conductive material;c. spraying the non-conductive material around the discrete locations ofthe conductive material to form a seamless bond between the conductiveand non-conductive materials; d. spraying a brazing material around eachdiscrete location of the conductive material; and e. curing the sprayedbrazing material around each discrete location of the conductivematerial to form a seamless joint between the non-conductive materialand the sprayed conductive material.
 2. The method as in claim 1,further comprising spraying the conductive material so that the discretelocations have a dimension less than approximately 500 microns.
 3. Themethod as in claim 1, further comprising spraying the conductivematerial so that the distance between discrete locations of conductivematerial is less than approximately 500 microns.
 4. The method as inclaim 1, further comprising spraying the conductive material so that thediscrete locations have a dimension less than approximately 500 micronsand the distance between discrete locations of conductive material isless than approximately 500 microns.
 5. The method as in claim 1,further comprising spraying the conductive material so that the distancebetween discrete locations of conductive material is less thanapproximately 5 microns.
 6. The method as in claim 1, further comprisingspraying the conductive material at discrete locations on the previouslysprayed conductive material.
 7. The method as in claim 1, furthercomprising connecting an electrode to each discrete location of theconductive material.
 8. The method as in claim 1, further comprisingconnecting an electrical sensor to each discrete location of theconductive material.
 9. A method for manufacturing a corrosion sensorcomprising: a. spraying a non-conductive material on a bond coat that isapplied to a metallic substrate; b. spraying a conductive material atdiscrete locations on the bond coat or on the non-conductive material;c. determining the thickness of the conductive material at discreetlocations; d. spraying the non-conductive material around the discretelocations of the conductive material to form a seamless bond between theconductive and non-conductive materials; e. spraying a brazing materialaround each discrete location of the conductive material; and f. curingthe sprayed brazing material around each discrete location of theconductive material to form a seamless joint between the non-conductivematerial and the conductive material.
 10. The method as in claim 9,further comprising spraying the conductive material so that the discretelocations have a dimension less than approximately 500 microns.
 11. Themethod as in claim 9, further comprising spraying the conductivematerial so that the distance between discrete locations of conductivematerial is less than approximately 500 microns.
 12. The method as inclaim 9, further comprising spraying the conductive material so that thediscrete locations have a dimension less than approximately 500 micronsand the distance between discrete locations of conductive material isless than approximately 500 microns.
 13. The method as in claim 9,further comprising spraying the conductive material so that the distancebetween discrete locations of conductive material is less thanapproximately 5 microns.
 14. The method as in claim 9, furthercomprising spraying the conductive material at discrete locations on thepreviously sprayed conductive material.
 15. The method as in claim 9,further comprising connecting an electrode to each discrete location ofthe conductive material.
 16. The method as in claim 9, furthercomprising connecting an electrical sensor to each discrete location ofthe conductive material.